Page Comparison

This page contains frequently asked questions related to *cables*.

*On this page:*

{toc}

h1. General FAQ

h2. How can I find initial cable geometry/length for more complicated loading, such as when various point loads are applied along the cable?

{open-question}

h2. Do I need to assign load representing the initial conditions to a cable whose geometry was determined using the Cable Geometry form?

*Expanded Question*: When the cable geometry form is used to determine the initial cable layout and length, I believe that one of the main objectives is to specify something like "initial tightness" of the cable. Would it be then correct to say that, in most of the cases, I would want to apply loads (such as DEAD + TARGET loads in the [Cable Watch & Learn video|videos:Cables video]) that will cause or match this tightness? Also, is correct to say that I would typically want to run subsequent nonlinear analysis to analyze for additional external loads (such as WIND loads in the Cable Watch & Learn video)?

*Answer*: Generally, yes. There is a relationship between initial shape and tension in the cable that depends on the cable length, the loading, and the flexibility of the supports. The cable drawing tool can calculate this for a single cable with fixed supports under distributed load. Full analysis must be used for cable systems, cables connected to flexible structures, or other loads. The best approach to be used depends on what you know and how the structure is to be built. If the cable length is known, simple nonlinear analysis is adequate. Otherwise, iteration on initial geometry or target force loading may be needed.

In any case, once the initial shape and tension is determined for the basic built structure, further analysis is needed for other loads, such as wind. Nonlinear analysis should be used whenever possible. The Watch & Learn video covers the basics quite well.

h2. In normal static linear analysis, is the cable stiffness considered in calculations or not?

[Nonlinear analysis DRAFT] is required to get meaningful results with the cable element. Linear analysis can be performed, but they should always use the stiffness from the end of a nonlinear static analysis case in which all cables are loaded by their self weight or other transverse loads. For cases where no transverse load is present on a slack cable elements, the program will internally assume a very small self-weight load in order to obtain a unique shape. However, it is better if you apply a realistic load for this purpose.

h2. Why do I see nonzero moment diagram on the cables in my model?

You may be modeling the cable using straight frame objects. If this is the case, please uncheck the "Model Cable Using Straight Frame Option" on the "Cable Geometry" form to model the cable as a catenary.

h2. How can I display the wind loading applied to the cables?

You are able to use the Display>Show Load Assign>Frame/Cable/Tendon menu command to display the wind loading on the cables. Please note that to generate wind loading on cable elements; you should define the auto load pattern to use Exposure from Frame Object.